Answer
Food
It's fast, but can't run.
This is a reference to fast food
It gets me ready for life.
Food gives you the necessary energy for everyday life.
Everyone can have it. It is sold everywhere.
Food is sold ubiquitously
It was here since Day 1.
Since beings have needed energy from outside sources, food has been available
So I went to find it, and just a bit of time later, I unlocked it
As explained by OP, buying food equates to "unlocking" it.
Alternative Answer
Light
It's fast, but can't run.
Light doesn't run but it travels fast (the fastest thing there is)
It gets me ready for life.
Light (especially sunlight) in the morning gets you ready to start your day.
Everyone can have it. It is sold everywhere.
Lightbulbs, matches, candles, torches are sold ubiquitously.
It was here since Day 1.
Light has been around since the dawn of time.
So I went to find it, and just a bit of time later, I unlocked it.
You unlocked your front door and light came flooding in.